1. Field of the Invention
The present invention relates to a digital image processing device capable of processing digital original image data representative of an original image to enlarge or reduce the original image.
2. Description of the Related Art
A digital image processing device is known in the field of enlarging or reducing an original image. The digital image processing device is connected to an input device for producing digital original image data representative of the original image. The digital image processing device receives the digital original image data produced by the input device and processes the original image data to thereby enlarge or reduce the original image. (The processing performed by the digital image processing device will be referred to as an "image enlarging/reducing processing", hereinafter).
The digital original image data include density data representative of the density of each of a multiplicity of picture elements which are arranged in a matrix consisting of a plurality of rows and a plurality of columns which extend perpendicularly to the rows. When the original image is a full-color image, a color at each picture element is determined by three sets of density data corresponding to three primary colors for that picture element. One example of the image enlarging/reducing processing employs an interpolation method. In order to enlarge the original image, the digital original image data for all the picture elements of the original image are subjected to an interpolation processing in which one or more new picture elements are inserted between each two adjacent original picture elements arranged in the rows and columns of the original image matrix. The original image is enlarged to a desired size, depending upon the number of the new picture elements interposed between the each adjacent two original picture elements. In order to reduce the original image, on the other hand, the digital original image data for all the picture elements are selectively subjected to the interpolation processing in which one new picture element is inserted between selected two adjacent original picture elements arranged in the rows and columns of the original image matrix. The original image is reduced to a desired size depending upon the number of the picture elements subjected to the interpolation method.
A conventional digital image processing device stores therein only a single algorithm or calculation program for performing the image enlarging/reducing processing which is determined dependently on its own hardware system. Accordingly, the conventional digital image processing device performs merely a single method of image enlarging/reducing processing for various kinds or types of digital original image data inputted from the input device.
For example, there has been proposed a digital image processing device of a type in which a single relatively simple calculation program is stored. According to the digital image processing device of this type, the digital original image data are subjected to a relatively simple image enlarging/reducing operation, so that the original image is roughly enlarged or reduced. In a concrete example of the digital image processing device of this type employing the interpolation method, the density of the new picture element to be inserted between two adjacent picture elements is determined through a relatively simple calculation of the density values of the two adjacent picture elements.
There has been also proposed a digital image processing device of another type in which a single relatively complicated calculation program is stored. According to the digital image processing device of this type, the digital original image data are subjected to a relatively complicated image enlarging/reducing operation, so that the original image is elaborately or minutely enlarged/reduced. In a concrete example of the digital image processing device of this type employing the interpolation method, the density value of the new picture element to be inserted into the selected two adjacent picture elements is determined through a relatively complicated calculation of the density values of the selected two adjacent picture elements.
In recent years, the input device has been greatly improved to produce the digital original image data representing the original image of high resolution and of high quality. In other words, the number of the digital original image data produced by the input device has been considerably increased. As a result, the data amount to be processed by the image processing device has been increased, and the processing rate of the image processing device has been greatly lowered.
For example, in the conventional digital image processing device of the type for elaborately enlarging/reducing the original image through the complicated calculation operation, if the data amount of the original image, i.e., the number of the digital original image data for the original image is large, even where the original image is to be enlarged by a small value of magnification or is to be reduced, time duration during which the enlarging/reducing processing is completed becomes long. In other words, the processing rate is lowered. Generally, the quality of the original image is not so deteriorated through the image enlarging process with the small value of magnification and through the image reducing process. Accordingly, it can be stated that the digital image processing device of this type performs unnecessary processings for the image enlarging operation with the small value of magnification and the image reducing operation.
To the contrary, in the conventional digital image processing device of the type for roughly enlarging/reducing the original image through the simple calculation operation, the time duration in which the image enlarging/reducing processing is completed is small, and therefore the processing rate is high. However, in the case where the original image is enlarged with the large value of magnification, the quality of the obtained image is greatly deteriorated. For example, the obtained image suffers from a jagging of straight or curved lines presented therein. In other words, through the image enlarging/reducing process, the straight or curved lines presented in the original image are erroneously converted into stepped lines which do not smoothly extend.
Furthermore, in recent years, the input device has been greatly improved to produce the digital original image data representative of the original image of a large size with high resolution. In this case, the number of the digital original image data produced by the input device becomes considerably large. If the digital original image data representative of the original image of the large size with the high resolution are processed by the conventional digital image processing device of the type for elaborately enlarging/reducing the original image, the period of time required for completing the image enlarging/reducing operation becomes considerably long. Accordingly, it becomes impossible to perform the image enlarging/reducing operation within a desired short period of time for the original image of the large size. On the other hand, if the digital original image data are processed by the conventional digital image processing device of the type for roughly enlarging/reducing the original image, the period of time required for completing the image enlarging/reducing operation is small. However, as described already, if the magnification value with which the original image is enlarged is high, the quality of the image obtained through the image enlarging/reducing operation is deteriorated due to the jagging phenomenon.